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WO2025195690A1 - Procédé de métrologie et dispositif de métrologie associé - Google Patents

Procédé de métrologie et dispositif de métrologie associé

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Publication number
WO2025195690A1
WO2025195690A1 PCT/EP2025/053868 EP2025053868W WO2025195690A1 WO 2025195690 A1 WO2025195690 A1 WO 2025195690A1 EP 2025053868 W EP2025053868 W EP 2025053868W WO 2025195690 A1 WO2025195690 A1 WO 2025195690A1
Authority
WO
WIPO (PCT)
Prior art keywords
incoherent
metrology
pitch
dipole
plane
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/EP2025/053868
Other languages
English (en)
Inventor
Willem Marie Julia Marcel COENE
Eibert Gerjan VAN PUTTEN
Patricius Aloysius Jacobus Tinnemans
Alexander Prasetya KONIJNENBERG
Robin Daniel BUIJS
Teunis Willem Tukker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ASML Netherlands BV
Original Assignee
ASML Netherlands BV
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Filing date
Publication date
Priority claimed from EP24164698.3A external-priority patent/EP4621485A1/fr
Application filed by ASML Netherlands BV filed Critical ASML Netherlands BV
Publication of WO2025195690A1 publication Critical patent/WO2025195690A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/70681—Metrology strategies
    • G03F7/70683—Mark designs
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/70681—Metrology strategies
    • G03F7/706831—Recipe selection or optimisation, e.g. select or optimise recipe parameters such as wavelength, polarisation or illumination modes
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/706843—Metrology apparatus
    • G03F7/706849—Irradiation branch, e.g. optical system details, illumination mode or polarisation control

Definitions

  • a lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate.
  • a lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
  • a lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).
  • a patterning device e.g., a mask
  • a layer of radiation-sensitive material resist
  • a substrate e.g., a wafer
  • a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm.
  • a lithographic apparatus which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.
  • EUV extreme ultraviolet
  • Low-k 1 lithography may be used to process features with dimensions smaller than the classical resolution limit of a lithographic apparatus.
  • ⁇ the wavelength of radiation employed
  • NA the numerical aperture of the projection optics in the lithographic apparatus
  • CD the “critical dimension” (generally the smallest feature size printed, but in this case half-pitch)
  • k1 is an empirical resolution factor.
  • the smaller k 1 the more difficult it becomes to reproduce the pattern on the substrate that resembles the shape and dimensions planned by a circuit designer in order to achieve particular electrical functionality and performance.
  • sophisticated fine-tuning steps may be applied to the lithographic projection apparatus and/or design layout.
  • RET resolution enhancement techniques
  • OPC optical proximity correction
  • RET resolution enhancement techniques
  • tight control loops for Confidential controlling a stability of the lithographic apparatus may be used to improve reproduction of the pattern at low k1.
  • a general term to refer to such tools may be metrology apparatuses or inspection apparatuses.
  • Holography tools enable this; however they require a reference beam and very stringent operation to ensure interference between the reference beam and measurement radiation beam.
  • Other phase retrieval methods may comprise an iterative retrieval of phase; however these are computationally demanding,
  • a metrology method comprising: obtaining metrology data relating to a measurement obtained by illuminating a periodic structure comprising at least one pitch with illumination comprising a wavelength and capturing at least a plurality of components of interest of said scattered radiation from said periodic structure at a image plane, said illumination comprising at least one incoherent dipole, each said at least one incoherent dipole comprising two mutually incoherent monopoles, said scattered radiation passing through at least one angularly resolved plane between said periodic structure and detection image plane; selecting said wavelength and each said at least one pitch such that mutually coherent interfering components of said components of interest are equidistant to an optical axis of said at least one angularly resolved plane; and determining a parameter of interest of the periodic structure from said scattered radiation.
  • FIG. 1 depicts a schematic overview of a lithographic apparatus
  • - Figure 2 depicts a schematic overview of a lithographic cell
  • Confidential - Figure 3 depicts a schematic representation of holistic lithography, representing a cooperation between three key technologies to optimize semiconductor manufacturing
  • - Figure 4 is a schematic illustration of a scatterometry apparatus
  • - Figure 5 comprises (a) a schematic diagram of a dark field scatterometer for use in measuring targets according to embodiments of the invention using a first pair of illumination apertures, (b) a detail of diffraction spectrum of a target grating for a given direction of illumination (c) a second pair of illumination apertures providing further illumination modes in using
  • the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range of about 5- 100 nm).
  • the term “reticle”, “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate.
  • FIG. 1 schematically depicts a lithographic apparatus LA.
  • the lithographic apparatus LA includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, a substrate support (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support in accordance with certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.
  • a radiation beam B e.g., UV radiation, D
  • the illumination system IL receives a radiation beam from a radiation source SO, e.g. via a beam delivery system BD.
  • the illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and/or other types of optical components, or any combination thereof, for directing, shaping, and/or controlling radiation.
  • the illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.
  • projection system PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and/or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.
  • the lithographic apparatus LA may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system PS and the substrate W – which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference. [00019]
  • the lithographic apparatus LA may also be of a type having two or more substrate supports WT (also named “dual stage”).
  • the substrate supports WT may be used in parallel, and/or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W.
  • the lithographic apparatus LA may comprise a measurement stage.
  • the measurement stage is arranged to hold a sensor and/or a cleaning device.
  • the sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B.
  • the measurement stage may hold multiple sensors.
  • the cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid.
  • the measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.
  • the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W.
  • the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position.
  • the first positioner PM and possibly another position sensor may be used to accurately position the patterning device MA with respect to the path of the radiation beam B.
  • Patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.
  • the substrate alignment marks P1, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions.
  • Substrate alignment marks P1, P2 are known as scribe-lane alignment marks when these are located between the target portions C.
  • the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as a lithocell or (litho)cluster, which often also includes apparatus to perform pre- and post-exposure processes on a substrate W.
  • a lithographic cell LC also sometimes referred to as a lithocell or (litho)cluster
  • these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH and bake plates BK, e.g. for conditioning the temperature of substrates W e.g. for conditioning solvents in the resist layers.
  • a substrate handler, or robot, RO picks up substrates W from input/output ports I/O1, I/O2, moves them between the different process apparatus and delivers the substrates W to the loading bay LB of the Confidential lithographic apparatus LA.
  • the devices in the lithocell which are often also collectively referred to as the track, are typically under the control of a track control unit TCU that in itself may be controlled by a supervisory control system SCS, which may also control the lithographic apparatus LA, e.g. via lithography control unit LACU.
  • a supervisory control system SCS which may also control the lithographic apparatus LA, e.g. via lithography control unit LACU.
  • inspection tools may be included in the lithocell LC.
  • An inspection apparatus which may also be referred to as a metrology apparatus, is used to determine properties of the substrates W, and in particular, how properties of different substrates W vary or how properties associated with different layers of the same substrate W vary from layer to layer.
  • the inspection apparatus may alternatively be constructed to identify defects on the substrate W and may, for example, be part of the lithocell LC, or may be integrated into the lithographic apparatus LA, or may even be a stand-alone device.
  • the inspection apparatus may measure the properties on a latent image (image in a resist layer after the exposure), or on a semi-latent image (image in a resist layer after a post-exposure bake step PEB), or on a developed resist image (in which the exposed or unexposed parts of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching).
  • a latent image image in a resist layer after the exposure
  • PEB post-exposure bake step
  • a developed resist image in which the exposed or unexposed parts of the resist have been removed
  • an etched image after a pattern transfer step such as etching.
  • the patterning process in a lithographic apparatus LA is one of the most critical steps in the processing which requires high accuracy of dimensioning and placement of structures on the substrate W.
  • three systems may be combined in a so called “holistic” control environment as schematically depicted in Figure 3.
  • the lithographic apparatus LA which is (virtually) connected to a metrology tool MET (a second system) and to a computer system CL (a third system).
  • the key of such “holistic” environment is to optimize the cooperation between these three systems to enhance the overall process window and provide tight control loops to ensure that the patterning performed by the lithographic apparatus LA stays within a process window.
  • the process window defines a range of process parameters (e.g. dose, focus, overlay) within which a specific manufacturing process yields a defined result (e.g. a functional semiconductor device) – typically within which the process parameters in the lithographic process or patterning process are allowed to vary.
  • the computer system CL may use (part of) the design layout to be patterned to predict which resolution enhancement techniques to use and to perform computational lithography simulations and calculations to determine which mask layout and lithographic apparatus settings achieve the largest overall process window of the patterning process (depicted in Figure 3 by the double arrow in the first Confidential scale SC1).
  • the resolution enhancement techniques are arranged to match the patterning possibilities of the lithographic apparatus LA.
  • the computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from the metrology tool MET) to predict whether defects may be present due to e.g. sub-optimal processing (depicted in Figure 3 by the arrow pointing “0” in the second scale SC2).
  • the metrology tool MET may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA to identify possible drifts, e.g. in a calibration status of the lithographic apparatus LA (depicted in Figure 3 by the multiple arrows in the third scale SC3).
  • a calibration status of the lithographic apparatus LA depictted in Figure 3 by the multiple arrows in the third scale SC3
  • Various tools for making such measurements are known, including scanning electron microscopes or various forms of metrology apparatuses, such as scatterometers.
  • Examples of known scatterometers often rely on provision of dedicated metrology targets, such as underfilled targets (a target, in the form of a simple grating or overlapping gratings in different layers, that is large enough that a measurement beam generates a spot that is smaller than the grating) or overfilled targets (whereby the illumination spot partially or completely contains the target).
  • underfilled targets a target, in the form of a simple grating or overlapping gratings in different layers, that is large enough that a measurement beam generates a spot that is smaller than the grating
  • overfilled targets whereby the illumination spot partially or completely contains the target.
  • the use of metrology tools for example an angular resolved scatterometer illuminating an underfilled target, such as a grating, allows the use of so-called reconstruction methods where the properties of the grating can be calculated by simulating interaction of scattered radiation with a mathematical model of the target structure and comparing the simulation results with those of a measurement.
  • Scatterometers are versatile instruments which allow measurements of the parameters of a lithographic process by having a sensor in the pupil or a conjugate plane with the pupil of the objective of the scatterometer, measurements usually referred as pupil based measurements, or by having the sensor in the image plane or a plane conjugate with the image plane, in which case the measurements are usually referred as image or field based measurements.
  • Such scatterometers and the associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, incorporated herein by reference in their entirety.
  • Aforementioned scatterometers ca measure in one image multiple targets from multiple gratings using light from soft x-ray and visible to near-IR wave range.
  • a metrology apparatus such as a scatterometer, is depicted in Figure 4. It comprises a broadband (white light) radiation projector 2 which projects radiation 5 onto a substrate W. The reflected or scattered radiation 10 is passed to a spectrometer detector 4, which measures a spectrum 6 (i.e. a measurement of intensity I as a function of wavelength ⁇ ) of the specular reflected radiation 10. From this data, the structure or profile 8 giving rise to the detected spectrum may be reconstructed by Confidential processing unit PU, e.g.
  • the scatterometer MT is an angular resolved scatterometer. In such a scatterometer reconstruction methods may be applied to the measured signal to reconstruct or calculate properties of the grating.
  • the scatterometer MT is a spectroscopic scatterometer MT.
  • the radiation emitted by a radiation source is directed onto the target and the reflected or scattered radiation from the target is directed to a spectrometer detector, which measures a spectrum (i.e. a measurement of intensity as a function of wavelength) of the specular reflected radiation.
  • the scatterometer MT is an ellipsometric scatterometer.
  • the ellipsometric scatterometer allows for determining parameters of a lithographic process by measuring scattered radiation for each polarization states.
  • Such metrology apparatus emits polarized light (such as linear, circular, or elliptic) by using, for example, appropriate polarization filters in the illumination section of the metrology apparatus.
  • a source suitable for the metrology apparatus may provide polarized radiation as well.
  • the scatterometer MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring asymmetry in the reflected spectrum and/or the detection configuration, the asymmetry being related to the extent of the overlay.
  • the two (typically overlapping) grating structures may be applied in two different layers (not necessarily consecutive layers), and may be formed substantially at the same position on the wafer.
  • the scatterometer may have a symmetrical detection configuration as described e.g. in co-owned patent application EP1,628,164A, such that any asymmetry is clearly distinguishable. This provides a straightforward way to measure misalignment in gratings. Further examples for measuring overlay error between the two layers containing periodic structures as target is measured through asymmetry of the periodic structures may be found in PCT patent application publication no. WO 2011/012624 or US Confidential patent application US 20160161863, incorporated herein by reference in its entirety. Other parameters of interest may be focus and dose.
  • Focus and dose may be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy) as described in US patent application US2011- 0249244, incorporated herein by reference in its entirety.
  • the targets may be measured in an underfilled mode or in an overfilled mode. In the underfilled mode, the measurement beam generates a spot that is smaller than the overall target. In the overfilled mode, the measurement beam generates a spot that is larger than the overall target. In such overfilled mode, it may also be possible to measure different targets simultaneously, thus determining different processing parameters at the same time.
  • Overall measurement quality of a lithographic parameter using a specific target is at least partially determined by the measurement recipe used to measure this lithographic parameter.
  • substrate measurement recipe may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns measured, or both.
  • the measurement used in a substrate measurement recipe is a diffraction-based optical measurement
  • one or more of the parameters of the measurement may include the wavelength of the radiation, the polarization of the radiation, the incident angle of radiation relative to the substrate, the orientation of radiation relative to a pattern on the substrate, etc.
  • One of the criteria to select a measurement recipe may, for example, be a sensitivity of one of the measurement parameters to processing variations. More examples are described in US patent application US2016-0161863 and published US patent application US 2016/0370717A1 incorporated herein by reference in its entirety.
  • Figure 5(a) presents an embodiment of a metrology apparatus and, more specifically, a dark field scatterometer.
  • a target T and diffracted rays of measurement radiation used to illuminate the target are illustrated in more detail in Figure 5(b).
  • the metrology apparatus illustrated is of a type known as a dark field metrology apparatus.
  • the metrology apparatus may be a stand-alone device or incorporated in either the lithographic apparatus LA, e.g., at the measurement station, or the lithographic cell LC.
  • An optical axis, which has several branches throughout the apparatus, is represented by a dotted line O.
  • light emitted by source 11 is directed onto substrate W via a beam splitter 15 by an optical system comprising lenses 12, 11 and objective lens 16.
  • lenses 12, 11 and objective lens 16 are arranged in a double sequence of a 4F arrangement.
  • a different lens arrangement can be used, provided that it still provides a substrate image onto a detector, and simultaneously allows for access of an intermediate pupil-plane for spatial-frequency filtering. Therefore, the angular range at which the radiation is incident on the substrate can be selected by defining a spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane, here referred to as a (conjugate) pupil plane or angularly resolved plane.
  • aperture plate 13 of suitable form between lenses 12 and 11, in a plane which is a back-projected image of the objective lens pupil plane.
  • aperture plate 13 has different forms, labeled 13N and 13S, allowing different illumination modes to be selected.
  • the illumination system in the present examples forms an Confidential off-axis illumination mode.
  • aperture plate 13N provides off-axis from a direction designated, for the sake of description only, as ‘north’.
  • aperture plate 13S is used to provide similar illumination, but from an opposite direction, labeled ‘south’.
  • Other modes of illumination are possible by using different apertures.
  • target T is placed with substrate W normal to the optical axis O of objective lens 16.
  • the substrate W may be supported by a support (not shown).
  • a ray of measurement radiation I impinging on target T from an angle off the axis O gives rise to a zeroth order ray (solid line 0) and two first order rays (dot-chain line +1 and double dot-chain line -1). It should be remembered that with an overfilled small target, these rays are just one of many parallel rays covering the area of the substrate including metrology target T and other features.
  • the aperture in plate 13 has a finite width (necessary to admit a useful quantity of light, the incident rays I will in fact occupy a range of angles, and the diffracted rays 0 and +1/-1 will be spread out somewhat. According to the point spread function of a small target, each order +1 and -1 will be further spread over a range of angles, not a single ideal ray as shown. Note that the grating pitches of the targets and the illumination angles can be designed or adjusted so that the first order rays entering the objective lens are closely aligned with the central optical axis. The rays illustrated in Figure 5(a) and 5(b) are shown somewhat off axis, purely to enable them to be more easily distinguished in the diagram.
  • both the first and second illumination modes are illustrated, by designating diametrically opposite apertures labeled as north (N) and south (S).
  • N north
  • S south
  • the incident ray I of measurement radiation is from the north side of the optical axis, that is when the first illumination mode is applied using aperture plate 13N
  • the +1 diffracted rays which are labeled +1(N)
  • the second illumination mode is applied using aperture plate 13S
  • the -1 diffracted rays (labeled 1(S)) are the ones which enter the lens 16.
  • a second beam splitter 17 divides the diffracted beams into two measurement branches.
  • optical system 18 forms a diffraction spectrum (pupil plane image) of the target on first sensor 19 (e.g. a CCD or CMOS sensor) using the zeroth and first order diffractive beams. Each diffraction order hits a different point on the sensor, so that image processing can compare and contrast orders.
  • the pupil plane image captured by sensor 19 can be used for focusing the metrology apparatus and/or normalizing intensity measurements of the first order beam.
  • the pupil plane image can also be used for many measurement purposes such as reconstruction.
  • optical system 20, 22 forms an image of the target T on sensor 23 (e.g.
  • an aperture stop 21 is provided in a plane that is conjugate to the pupil-plane.
  • Aperture stop 21 functions to block the zeroth Confidential order diffracted beam so that the image of the target formed on sensor 23 is formed only from the -1 or +1 first order beam.
  • the images captured by sensors 19 and 23 are output to processor PU which processes the image, the function of which will depend on the particular type of measurements being performed. Note that the term ‘image’ is used here in a broad sense. An image of the grating lines as such will not be formed, if only one of the -1 and +1 orders is present. [00042]
  • the particular forms of aperture plate 13 and field stop 21 shown in Figure 5 are purely examples.
  • the aperture plate 13 may comprise a number of aperture patterns formed around a disc, which rotates to bring a desired pattern into place. Note that aperture plate 13N or 13S can only be used to measure gratings oriented in one direction (X or Y depending on the set-up).
  • a metrology device may comprise a holographic microscope such as a digital holographic microscope (DHM) or digital dark-field holographic microscope.
  • a holographic microscope such as a digital holographic microscope (DHM) or digital dark-field holographic microscope.
  • light may be used to create an image (e.g., at one or both of an image plane or pupil plane/angularly resolved plane) of a structure on a substrate.
  • Such tools may measure the intensity or amplitude (or related measurement parameter such as diffraction efficiency) of the detected light, e.g., after having been scattered by the structure, and use this to determine one or more parameters of interest of the structure.
  • it may be beneficial to know the complex field (i.e., amplitude and phase) of the light scattered by the structure.
  • There are a number of present methods which enable the phase to be determined, in addition to the measured intensity/amplitude.
  • Another known method comprises performing multiple measurements under various conditions (e.g., different focus levels) and reconstructing the complex field of the scattered light using an iterative algorithm (e.g. as described in WO2021/121733, incorporated herein by reference).
  • an iterative algorithm e.g. as described in WO2021/121733, incorporated herein by reference.
  • such methods are computationally very demanding/expensive and can be slow as a consequence, particularly as the accuracy of the retrieved phase is required to be higher in metrology Confidential than for more conventional phase retrieval applications such as microscopy and which require only the formation of an image.
  • the time constraint may be replaced/implemented by locating a mask in the pupil plane (i.e., angularly resolved plane), such that the time coordinate t becomes the pupil coordinate, and the angular frequency coordinate ⁇ becomes the sensor/camera (image plane) coordinate.
  • the Kramers-Kronig relationship comprises a linear integral transform (in essence a convolution operation)
  • the (one-dimensional) Kramers-Kronig expression(s) expressed in terms of Fourier transforms, may be extended into a two-dimensional analysis; i.e., the two dimensions of the pupil plane/image plane.
  • the pupil edge may be used as the mask, e.g., by centering the specular beam (or each diffracted/scattered beam of interest in a dark-field embodiment) on the pupil edge in the pupil plane such that the edge clips (i.e., blocks) half of the beam.
  • illumination which is not coherent, e.g., partial coherent radiation.
  • many present metrology apparatuses e.g., such as that illustrated in Figure 5(a)
  • already use partial coherent illumination and it is desirable to use such apparatuses for non-iterative phase retrieval without significant hardware/source changes or spatial filtering of the light source, the latter option coming at the expense of light throughput.
  • Arrangements described herein may be used for example, in diffraction based metrology such as diffraction based overlay (DBO) or diffraction based focus (DBF) metrology.
  • DBO diffraction based overlay
  • DBF diffraction based focus
  • the proposed method may comprise properly selecting wavelength and target pitch (e.g., ⁇ /p ratio) to enable suitable reconstruction of the electric field.
  • FIG. 6(a) illustrates such a target 60 which may be measured with the targets overfilled, i.e., fully comprised within a measurement spot 61 during a measurement.
  • Target 60 may comprise one or more sub-targets 62, 63, 64, 65.
  • the target 60 may comprise a pair of sub-targets per measurement direction; i.e., a first pair of sub-targets 62, 64 for measuring X- direction overlay and a second pair of sub-targets 63, 65 for measuring Y-direction overlay.
  • Each of the sub-targets may comprise a respective periodic structure or grating in each of the two layers being compared in the overlay measurement; i.e., a first grating or bottom grating G1 and a second grating or top grating G2. All the gratings comprise the same pitch p, i.e., such that the target 60 comprises a single pitch p.
  • Each sub-target of a pair of sub-targets may comprise a different bias, e.g., sub-targets 62, 63 may comprise a bias +d and sub-targets 64, 65 may comprise a bias –d.
  • Other arrangements described herein may be used in cDBO (continuous-DBO) metrology.
  • Figure 6(b) illustrates such a target 60’.
  • target 60’ may comprise one or more sub-targets, e.g., four sub-targets 62’, 63’, 64’, 65’ arranged as a pair of sub-targets per measurement direction; i.e., a first pair of sub-targets 62’, 64’ for measuring X-direction overlay and a second pair of sub-targets 63’, 65’ for measuring Y-direction overlay.
  • each of the sub-targets may comprise a respective periodic structure or grating in each of the two layers being compared in the overlay measurement; i.e., a first grating G1’ and a second grating G2’.
  • the second grating G2’ and first grating G1’ now have respective different pitches p 1, p 2 .
  • These pitches are interchanged between top and bottom Confidential gratings for the sub-targets of each directional pair; e.g., as shown here, the first grating G1’ with pitch p1 is the top grating for sub-target 64’ and the bottom grating for sub-target 62’ and the second grating G2’ with pitch p2 is the top grating for sub-target 62’ and the bottom grating for sub-target 64’.
  • These two sub-targets are typically referred to as “W” and “M” sub-targets, indicative of the interchange of the two pitches.
  • a “continuous bias” (e.g., a bias which continuously varies along the sub-target) is realized between top and bottom grating, which gives rise to a typical Moiré fringe in cDBO dark-field images.
  • Overlay may be determined by comparing the respective phases of these Moiré fringes for the “W” and “M” sub-targets, e.g., comparing a corresponding one of the +1 and -1 diffraction orders, or the +1 and -1 diffraction orders summed together, from each of these sub- targets.
  • peripheral structure may comprise a compound periodic structure comprising respective gratings in two (or more) layers and/or multiple sub-targets (each having respective gratings in two or more layers) for measuring in different measurement directions and/or comprising different biases or grating order.
  • single layer targets are also possible, e.g., in a focus metrology context.
  • Figure 7 illustrates a proposed alternative exit pupil or detection pupil (angularly resolved plane) arrangement to those presently used, which enables greater flexibility in that it provides for the option of using partial coherent illumination rather than fully coherent illumination.
  • a dipole illumination is used, resulting in respective specular beams 700a, 700b in two opposed regions within the exit pupil 705 (i.e., representing the detection NA, with a value ⁇ for the detection NA described by the radius of the pupil).
  • the specular beams 700a, 700b may be diagonally opposed with respect to a pupil coordinate system ⁇ , ⁇ defined by the measurement directions X, Y, e.g., 45 degrees with respect to this pupil coordinate system).
  • One each of the +1X diffraction order 710, -1X diffraction order 715, +1Y diffraction order 720 and -1Y diffraction order 725 is captured within the detection NA 705.
  • a diagonally oriented two-fold wedge having an edge 730 separating the exit-pupil into two equally sized halves allows simultaneous imaging of the two specular beams 700a, 700b and four diffraction orders 710, 715, 720, 725.
  • the shading does not indicate that the two specular beams 700a, 700b and their respective diffraction orders are different, only to illustrate which captured diffraction order relates to which of the specular beams 700a, 700b (e.g., +1X diffraction order 710 and -1Y diffraction order 725 are part of the same diffraction pattern as specular beam 700a and, -1X diffraction order 715 and +1Y diffraction order 720 are part of the same diffraction pattern as specular beam 700b).
  • the diffracted orders are represented as square solely to differentiate then from the specular beams in the drawing.
  • the proposed methods may enable and/or result in aberration correction; e.g., the proposed methods may result in the measured signals being insensitive (or less sensitive) to at least even order aberrations.
  • the proposed methods may also result in the measured signals being insensitive (or less sensitive) to at least odd order aberrations.
  • the methods may enable odd order aberrations being correctable in an additional step.
  • an illumination configuration comprising a single dipole comprising two mutually incoherent monopoles (which is referred to herein as an “incoherent dipole”), or an incoherent dipole per measurement direction.
  • an incoherent dipole may comprise a dipole for which its constituent monopoles are mutually incoherent. Where there are two incoherent dipoles, one per measurement direction, then all four monopoles may be mutually incoherent.
  • Each of the monopoles per dipole may be equidistant to an optical axis (e.g., center of the NA) of the system.
  • the monopoles per dipole may be symmetrically opposite within the NA, e.g., both equidistant to an optical axis and arranged linearly with the optical axis. It can be appreciated that each of the mutually incoherent monopoles of the at least one dipole all generate a respective single-sided spectrum in the exit pupil/detection pupil.
  • the wavelength of the measurement illumination i.e., the one incoherent dipole or the two incoherent dipoles
  • the one or more pitches of a target are selected such that mutually coherent interfering components of the scattered radiation from the target are equidistant to the optical axis, and optionally symmetrically opposite within the NA.
  • mutually coherent interfering components of the scattered radiation comprise components of the scattered radiation which are to be interfered towards a fringe-based pattern in the measured image to determine the parameter of interest (e.g., overlay or focus).
  • the wavelength and each said one or more pitches may be selected such that all components of interest of said scattered radiation are scattered to only two scattering locations per measurement direction within said at least one angularly resolved plane.
  • components of interest of Confidential said scattered radiation comprise all diffraction orders of interest (e.g., two first diffraction orders per measurement direction, e.g., a positive first order and a negative first order) and, for the bright-field embodiments only, also the zeroth orders.
  • all components of interest are scattered to only four scattering locations within said at least one angularly resolved plane.
  • at least one of said two scattering locations per measurement direction receive two mutually incoherent components of said components of interest.
  • the mutually coherent interfering components of the scattered radiation may comprise (for each illumination monopole) a zeroth order (specular) component and a corresponding, mutually coherent first order (both comprising a single-sided spectrum).
  • a zeroth order (specular) component and a corresponding, mutually coherent first order (both comprising a single-sided spectrum).
  • the illumination wavelength and target pitch may be selected such that the distance between the two monopoles of each incoherent dipole is ⁇ /p (in terms of NA) or 1/p (in terms of spatial frequency, i.e., NA/ ⁇ ).
  • each specular beam will overlap in the detection (exit) pupil plane (intermediate angularly resolved plane) with a first order of which it is mutually incoherent (i.e., corresponding to the other monopole of the dipole).
  • ⁇ DBO arrangements are possible, however; e.g., another embodiment may use a single illumination dipole for measuring in two measurement directions. In such an arrangement, the dipole position, wavelength and target pitch may be selected such that mutually incoherent first orders overlap in the pupil plane.
  • the -1X order corresponding to one illumination monopole may overlap with the -1Y order corresponding to the other monopole and the +1X order corresponding to one illumination monopole may overlap with the +1Y order corresponding to the other monopole.
  • the mutually coherent interfering components of the scattered radiation may comprise (for each illumination monopole) a zeroth order (specular) component and in this embodiment, two corresponding, mutually coherent first orders (one per measurement direction), with each of these mutually coherent interfering components being equidistant from the optical axis.
  • a proposed cDBO example may comprise a dark-field metrology technique, where the zeroth order beams are blocked at the detection pupil plane (angularly resolved plane).
  • the dipole positions, wavelength and pitches may be chosen such that mutually incoherent first orders (of which there will be two per target, a respective order for each of the constituent target pitches) overlap in the detection pupil plane.
  • Such an arrangement means that there are (per-direction) two scattering locations in the detection pupil plane.
  • Each of the scattering locations receives one first diffraction order resulting from interaction of a first monopole of the incoherent dipole and one of the target pitches and another first diffraction order resulting from interaction of a second monopole of the incoherent dipole and the other target pitch.
  • These scattering locations may be equidistant (at least per direction) from the optical axis, Confidential and may be symmetrically opposed within the NA, such that the mutually coherent interfering components, which in this case comprise a first order resultant from a first target pitch and a first order resultant from a second target pitch which both correspond to a common illumination monopole, are also equidistant from the optical axis, and optionally may be symmetrically opposed within the NA.
  • Figure 8 illustrates an illumination pupil 800 or illumination angularly resolved plane (in spatial frequency space ⁇ , ⁇ ) describing an illumination arrangement which may be used in at least some ⁇ DBO and cDBO embodiments.
  • the illumination pupil comprises a first incoherent dipole 805a, 805b for metrology in a first measurement direction (e.g., the X-direction) and a second incoherent dipole 805c, 805d for metrology in a second measurement direction (e.g., the Y-direction).
  • Each respective dipole is substantially aligned orthogonal to the grating lines of the respective sub-targets of the overlay target it is to measure.
  • the first incoherent dipole 805a, 805b which is used for X-direction parameter of interest metrology, is substantially aligned orthogonal to the grating lines of the X-direction sub-targets and the second incoherent dipole 805c, 805d, which is used for Y- direction parameter of interest metrology, is substantially aligned orthogonal to the grating lines of the Y-direction sub-targets).
  • the incoherent dipoles are substantially aligned with an apparatus coordinate system defined by the two measurement directions.
  • substantially aligned does not require being precisely aligned, and substantially aligned may be understood to be within 10 degrees, within 5 degrees, within 3 degrees, within 2 degrees or within 1 degree of exact alignment.
  • All four monopoles 805a, 805b, 805c, 805d are mutually incoherent (in the drawing, each line style/shade combination signifies a different coherence state). This configuration may be similar to the dipole and quad illumination as used in lithographic scanners.
  • FIG. 9 is a schematic of the detection pupil (angularly resolved plane) for a ⁇ DBO embodiment using the illumination pupil of Figure 8.
  • each of the mutually incoherent specular reflections 905a, 905b, 905c, 905d is overlapped in the detection pupil 900 with a respective mutually incoherent first diffraction order 915a, 915b, 915c, 915d.
  • a first mutually incoherent specular reflection pair 905a, 905b corresponds to the first incoherent dipole 805a, 805b and a second mutually incoherent specular reflection pair 905c, 905d corresponds to the second incoherent dipole 805c, 805d.
  • Confidential More specifically, for each mutually incoherent specular reflection pair, each constituent specular reflection overlaps with a first order diffraction with which it is incoherent (i.e., a first order diffraction which corresponds to the other specular reflection of the specular reflection pair).
  • each scattered radiation component signifies its coherence, i.e., such that specular reflection 905a is mutually coherent with diffraction order 915a (both resulting from the illumination monopole 805a) and no other of the scattered radiation components 905b, 905c, 905d, 915b, 915c, 915d; specular reflection 905b is mutually coherent with diffraction order 915b (both resulting from the illumination monopole 805b) and no other of the scattered radiation components etc..
  • this detection pupil 900 When this detection pupil 900 is imaged (at a detector plane or image plane), the components which are mutually coherent will interfere, e.g., respective sets of mutually coherent interfering components comprising a specular reflection and corresponding diffraction order (e.g., components 905a, 915a will interfere, as will components 905b, 915b, components 905c, 915c and components 905d, 915d).
  • the illumination monopoles, specular reflections and diffraction orders of interest are close to the edge of the detection pupil. In this manner, it is possible to provide for a large range for ⁇ / ⁇ ⁇ 2NA (actually, a bit smaller).
  • the symmetry in the detection pupil enables digital aberration correction to be performed.
  • the proposed symmetry of the mutually coherent interfering components (or at least their equidistance from the optical axis 820) makes it possible to disentangle the distilled complex-valued field into a product of a sample factor (which is a sum of two contributions from each of the monopoles of a incoherent dipole) and an aberration factor, such that the latter can be corrected for by deconvolution in a digital post-processing step.
  • Figure 10 illustrates the relationship between object spectrum and image spectrum.
  • Figure 10(a) illustrates the object spectrum in the detection pupil, corresponding to the detection pupil of Figure 9, and
  • Figure 10(b) illustrates the corresponding image spectrum.
  • Figure 10(b) illustrates the corresponding image spectrum.
  • ⁇ ⁇ ⁇ ⁇ ⁇ ! ⁇ ⁇ ⁇
  • ⁇ is the spatial frequency space.
  • a method for determining a value for a parameter of interest such as overlay from the detected image may comprise Fourier filtering one of the diffraction orders of the image spectrum (or alternatively performing a phase-retrieval via a Hilbert transform) to determine the electric field, performing an aberration correction on the complex valued result of the Fourier filtering, and inferring the parameter of interest from the aberration corrected field.
  • Fourier-filtering of the +1 st order (or -1 st order, the choice is arbitrary) of the image spectrum may comprise determining a filter region over which the Fourier filter extends.
  • the extent of the Fourier Confidential filter depends inter alia on the size of the sub-targets in the metrology target: the smaller the sub-target, the larger the extent of its first orders in Fourier space (with the typical Fraunhofer-like patterns characteristic of diffraction by finite pads).
  • BF bright-field
  • the first order of the BF image comprises information on the phases of the first orders as well as zeroth orders of the object field, with there being (in this embodiment) two superimposed interferences between zeroth and first orders.
  • This method takes advantage of the single-sided nature of the diffraction information of the object field(s) (only +1 st order object field information or only -1 st order object field information for a given monopole).
  • the Fourier-filtered image spectrum ⁇ & ! for the +1 st order may be described by: ⁇ !
  • the aberration correction on the complex-valued information that results as output from Fourier-filtering step comprises the aberration function which applies to both the zeroth order and its related (mutually coherent) first order of the object field for each of the two monopoles of the considered dipole (X or Y). Because of the aforementioned symmetry in the detection pupil a single aberration correction can be applied (e.g., via deconvolution) which is common to both monopole contributions, to yield the aberration-corrected field. Note that the aberration term corrected by deconvolution may relate only to the odd-order aberrations; even order aberrations may be canceled in the overlay inference as described below.
  • the (e.g., aberration-corrected) field can be used to determine the parameter of interest (e.g., per measurement direction).
  • the aberration-corrected field is a superposition of two contributions from the two monopoles of the considered dipole.
  • overlay can be inferred in using a simple overlay DBO-model, for which the target comprises (per direction) two biased sub-targets with overlay biases ⁇ (i.e., as illustrated in Figure 6(a).
  • this is only an example and other (e.g., a more sophisticated) models may be used, including those which may use more than two biased sub- targets per direction.
  • Such an overlay derivation may be impaired by zeroth order light leaking into the first orders of the image spectrum, particularly when the sub-target windows are oriented parallel to the grating lines.
  • an alternative approach may use a Hilbert transform for phase retrieval (complex-valued field determination).
  • is the zeroth order amplitudes for both monopoles (i.e., assumed equal for both monopoles): [00087] Applying the Hilbert Transform onto the
  • the wavelength and target pitch is such that the two monopoles of each incoherent dipole (and therefore the two reflections of each specular reflection pair) are separated by (a now smaller) 1/p in spatial frequency space.
  • specular reflection 905a’ is mutually coherent with diffraction order 915a’ (both resulting from the same illumination monopole) and no other of the scattered radiation components 905b’, 905c’, 905d’, 915b’, 915c’, 915d’;
  • specular reflection 905b’ is mutually coherent with diffraction order 915b’ and no other of the scattered radiation components etc.
  • unwanted diffraction orders are diffracted into the regular detection pupil 900.
  • These unwanted diffraction orders may comprise one or both of: a 2 nd diffraction order on the same side of each diffraction order of interest and/or the opposite first diffraction order of each diffraction order of interest.
  • Figure 11(b) illustrates an arrangement for blocking these unwanted diffraction orders 1100 (shown with crosses, only one labeled).
  • a method comprises providing a block 1105 defining an appropriately sized aperture 1110 so as to pass the wanted components while blocking the unwanted diffraction orders 1100.
  • a configurable aperture arrangement comprising multiple detection apertures of different sizes (e.g., mounted on an aperture wheel) or a configurable iris mechanism may be provided such that an appropriate aperture sized can be selected in dependence of the ⁇ / ⁇ ratio.
  • Such a configurable aperture arrangement may be located at an intermediate angularly resolved plane which is physically reachable (e.g., where the wedge is currently located in typical ⁇ DBO overlay metrology as presently performed).
  • the configurable aperture arrangement may be located at the same location as that of aperture stop 21 on Figure 5(a) (shown there for blocking a zeroth order in a conventional dark-field measurement).
  • Figure 12 illustrates an alternative ⁇ DBO example, wherein the four scattering locations are arranged in a square arrangement.
  • Figure 12(a) shows a proposed illumination pupil 1200 for such an embodiment comprises a single incoherent dipole 1205a, 1205b for measuring targets of two mutually perpendicular measurement directions.
  • the incoherent dipole 1205a, 1205b has an angle magnitude substantially 45 degrees with respect to the two measurement directions (e.g., an apparatus coordinate system defined by the two measurement directions).
  • the two monopoles of the dipole 1205a, 1205b are equidistant at distance d from the optical axis 1220.
  • Figure 12(a) also shows the corresponding detection pupil 1225.
  • the ⁇ / ⁇ ratio is selected such that each diffraction order of interest 1215a, 1215b, 1215c, 1215d (as with previous embodiments, one first order per monopole, per direction) is diffracted to one of a pair of scattering Confidential locations in the detection pupil 1225, the pair of scattering locations being aligned perpendicular to the specular reflection 1210a, 1210b from the dipole illumination.
  • each of these scattering locations and the scattering locations which receive the specular reflection together form a square arrangement centered on the optical axis 1220, with each of the four scattering locations at a corner of the square and equidistant d from the optical axis 1220.
  • the arrangement is such that the mutually incoherent overlapping components are no longer a zeroth order and a first order, but two mutually incoherent first orders (one per measurement direction).
  • an X diffraction order 1215b (corresponding to illumination monopole 1205b) overlaps a Y diffraction order 1215d (corresponding to illumination monopole 1205a).
  • a Y diffraction order 1215a (corresponding to illumination monopole 1205b) overlaps an X diffraction order 1215c (corresponding to illumination monopole 1205a).
  • the metrology method in this embodiment is still a bright-field measurement.
  • the mutually coherent interfering components comprise a first set of mutually coherent interfering components 1210a, 1215c, 1215d, and a second set of mutually coherent interfering components 1210b, 1215a, 1215b.
  • Each component of each set of mutually coherent interfering components is equidistant d from the optical axis 1220.
  • Figure 12(b) illustrates that the arrangement illustrated in Figure 12(a) can be adapted to accommodate a greater range of ⁇ / ⁇ ratios, in manner similar in principle to that illustrated in Figure 11(a).
  • the illumination dipole 1205a’, 1205b’ can be moved closer to the optical axis 1220 with the monopoles remaining equidistant d’ to the optical axis 1220.
  • the ⁇ / ⁇ ratio should then be configured to retain the square arrangement described, i.e., such that mutually incoherent diffraction orders 1215a’, 1215c’ overlap at a first scattering location and mutually incoherent diffraction orders 1215b’, 1215d’ overlap at a second scattering location, the first and second scattering locations also being at the distance d’ from the optical axis.
  • Figure 13(a) illustrates a detection pupil 1300 arrangement for cDBO metrology, or more generally metrology where the measured target comprises two pitches, wherein a single sub-target thereof may comprise a first pitch for the top layer and a second pitch for the bottom layer.
  • the illumination profile may comprise the illumination pupil 800 illustrated in Figure 8, comprising an incoherent dipole comprising two mutually incoherent monopoles per measurement direction (e.g., where all four monopoles are mutually incoherent).
  • the method disclosed for cDBO is a dark-field method in that all of the specular beams 1305a, 1305b, 1305c, 1305d corresponding to the illumination monopoles 805a, 805b, 805c, 805d are blocked before the detector, e.g., in a angularly resolved plane.
  • Any suitable mask or zeroth order block may be Confidential used to perform this blocking, such as zeroth order block 1330 illustrated in Figure 13, or an annular block 21 as illustrated in Figure 5(a).
  • the two target pitches ⁇ $ , ⁇ V means that, per illumination monopole, there are two first orders of interest (i.e., respective two first orders on one side of each specular beam, one corresponding to each of the two pitches).
  • the proposed method comprises choosing the two ratios ⁇ / ⁇ $ , ⁇ / ⁇ V such that, per measurement direction, the four diffraction orders of interest are each diffracted to one of two scattering locations 1315a, 1315b, 1315c, 1315d, the scattering locations being equidistant to the optical axis 1320 (e.g., symmetrically arranged within the detection pupil 1300, and in addition, optionally positioned at two positions that have mutual point-inversion symmetry with respect to the point or location of the optical axis in the detection pupil or exit pupil).
  • the optical axis 1320 e.g., symmetrically arranged within the detection pupil 1300, and in addition, optionally positioned at two positions that have mutual point-inversion symmetry with respect to the point
  • Figure 13(b) illustrates the concept more clearly (showing one measurement direction only for clarity).
  • scattering location 1315a, 1315b there are two mutually incoherent diffraction orders, one per target pitch, each corresponding to a different illumination monopole of the incoherent dipole illumination.
  • scattering location 1315a receives one diffraction order resulting from interaction of illumination monopole 805a and first pitch ⁇ $ and one diffraction order resulting from interaction of illumination monopole 805b and second pitch ⁇ V .
  • scattering location 1315b receives one diffraction order resulting from interaction of illumination monopole 805a and second pitch ⁇ V and one diffraction order resulting from interaction of illumination monopole 805b and first pitch ⁇ $.
  • the mutually coherent interfering components of the scattered radiation comprise mutually coherent first orders per measurement direction, i.e., the two diffraction orders, one per target pitch, corresponding to one illumination monopole.
  • the diffraction orders corresponding to illumination monopole 805a and respectively diffracted over diffraction vectors + ⁇ $ and + ⁇ V form a first set or pair of mutually coherent interfering components
  • the diffraction orders corresponding to illumination monopole 805b and respectively diffracted over diffraction vectors ⁇ $ and ⁇ V form a second set or pair of mutually coherent interfering components.
  • Figure 13(c) is an image spectrum of the captured dark-field image, comprising a direct component DC and two amplitude components AC per measurement direction.
  • the parameter of interest may be derived from (an arbitrarily chosen) one of the amplitude components AC per direction (i.e., as depicted: either the right or left monopole for measurement in X, or the top or bottom monopole for measurement in Y).
  • the capture image comprises a sum of two dark-field images, as generated by the monopoles at the left hand side and the right hand side, respectively.
  • there are two interfering diffraction orders symmetrically positioned with respect to the optical axis.
  • dZ-vibration of the stage is similar to an instantaneous defocus; the effect of a defocus for these two symmetrically aligned orders that will be used further for dark-field imaging leads to an equal phase shift (defocus is in fact an even spherical aberration), which cancels to zero upon two-beam interference.
  • the same argument holds for multiple wavelengths within a small but finite bandwidth ⁇ (which can also be seen as effective focal spreading due to the product of ⁇ and dZ in the defocus-induced phase change).
  • Working in Fourier space enables analysis of the respective phase-shifts that can be observed in the dipole dark-field images of the respective first sub-target or M sub-target and second sub-target or W sub-target.
  • the left monopole generates +first orders for first spatial frequency ⁇ $ and second spatial frequency ⁇ V
  • the right monopole generates -first orders for these spatial frequencies ⁇ $ , ⁇ V .
  • Each monopole generates these two diffraction orders which interfere with each other, and are summed together for each of the M and W sub-targets.
  • Figure 14(a) illustrates a detection pupil 1400 where the incoherent dipoles and therefore the zeroth orders 1405a, 1405b, 1405c, 1405d (again blocked by stop 1430) are off-axis. All four monopoles are again mutually incoherent.
  • the angle of the incoherent dipoles with respect to the X/Y coordinate system may be any angle (e.g., with the two dipoles maintained mutually orthogonal), as it can be appreciated that the mutually coherent interfering components will be equidistant to the optical axis 1420 for all angles.
  • the mutually coherent interfering components in the example comprise a first pair (X-direction) 1415a and 1415b, a second pair (X-direction) 1415c and 1415d, a third pair (Y-direction) 1417a and 1417b and a fourth pair (Y-direction) 1417c and 1417d.
  • Figure 14(b) is an equivalent Figure to that of Figure 13(b) for this embodiment.
  • the terms “left” monopole and “right” monopole are simply explanatory labels used to distinguish the monopoles of the X direction incoherent dipole with reference to the optical axis as illustrated in the Figure (i.e., on the left side or right side of the optical axis as drawn). More generally, the “left” monopole and “right” monopole are a first monopole of the first (X-direction) incoherent dipole and a second monopole of the first incoherent dipole.
  • the terms “left” and “right” may be replaced by “top” and “bottom” (more generally a first monopole of the second incoherent dipole and a second monopole of the second (Y-direction) incoherent dipole).
  • An illumination mode selector module is a form of spatial light modulation device (for example a multi-mirror array, MMA) or spatial light configuration device which enables control/configuration of the spatial pattern of the illumination pupil (i.e., the illumination configuration).
  • the inferred parameter of interest is (at least in some embodiments) insensitive, or less sensitive, to in-plane and/or out-of-plane stage vibration: the insensitivity for out-of-plane vibrations is realized through the symmetric alignment of the interfering diffraction orders with respect to the optical axis in the exit or Confidential detection pupil, whereas the insensitivity for in-plane vibrations is realized to the further combination (subtraction) of phases of the respective phases for W and M pads in the cDBO overlay target.
  • Figure 15 is a block diagram that illustrates a computer system 1500 that may assist in implementing the methods and flows disclosed herein.
  • Computer system 1500 includes a bus 1502 or other communication mechanism for communicating information, and a processor 1504 (or multiple processors 1504 and 1505) coupled with bus 1502 for processing information.
  • Computer system 1500 also includes a main memory 1506, such as a random access memory (RAM) or other dynamic storage device, coupled to bus 1502 for storing information and instructions to be executed by processor 1504.
  • Main memory 1506 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 1504.
  • Computer system 1500 further includes a read only memory (ROM) 1508 or other static storage device coupled to bus 1502 for storing static information and instructions for processor 1504.
  • ROM read only memory
  • a storage device 1510 such as a magnetic disk or optical disk, is provided and coupled to bus 1502 for storing information and instructions.
  • Computer system 1500 may be coupled via bus 1502 to a display 1512, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user.
  • a display 1512 such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user.
  • An input device 1514 is coupled to bus 1502 for communicating information and command selections to processor 1504.
  • cursor control 1516 such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor 1504 and for controlling cursor movement on display 1512.
  • This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane.
  • a touch panel (screen) display may also be used as an input device.
  • One or more of the methods as described herein may be performed by computer system 1500 in response to processor 1504 executing one or more sequences of one or more instructions contained in main memory 1506. Such instructions may be read into main memory 1506 from another computer- readable medium, such as storage device 1510. Execution of the sequences of instructions contained in main memory 1506 causes processor 1504 to perform the process steps described herein.
  • processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory 1506.
  • hard-wired circuitry may be used in place of or in combination with software instructions.
  • description herein is not limited to any specific combination of hardware circuitry and software.
  • computer-readable medium refers to any medium that participates in providing instructions to processor 1504 for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media.
  • Non-volatile media include, for example, optical or magnetic disks, such as storage device 1510.
  • Volatile media include dynamic memory, such as main memory 1506.
  • Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 1502.
  • Transmission media can also Confidential take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications.
  • RF radio frequency
  • IR infrared
  • Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.
  • Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor 1504 for execution.
  • the instructions may initially be borne on a magnetic disk of a remote computer.
  • the remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem.
  • a modem local to computer system 1500 can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal.
  • An infrared detector coupled to bus 1502 can receive the data carried in the infrared signal and place the data on bus 1502.
  • Bus 1502 carries the data to main memory 1506, from which processor 1504 retrieves and executes the instructions.
  • Computer system 1500 also preferably includes a communication interface 1518 coupled to bus 1502.
  • Communication interface 1518 provides a two-way data communication coupling to a network link 1520 that is connected to a local network 1522.
  • communication interface 1518 may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line.
  • ISDN integrated services digital network
  • communication interface 1518 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN.
  • LAN local area network
  • Network link 1520 typically provides data communication through one or more networks to other data devices.
  • network link 1520 may provide a connection through local network 1522 to a host computer 1524 or to data equipment operated by an Internet Service Provider (ISP) 1526.
  • ISP 1526 in turn provides data communication services through the worldwide packet data communication network, now commonly referred to as the “Internet” 1528.
  • Internet 1528 uses electrical, electromagnetic or optical signals that carry digital data streams.
  • Computer system 1500 may send messages and receive data, including program code, through the network(s), network link 1520, and communication interface 1518.
  • a server 1530 might transmit a requested code for an application program through Internet 1528, ISP 1526, local Confidential network 1522 and communication interface 1518.
  • One such downloaded application may provide for one or more of the techniques described herein, for example.
  • the received code may be executed by processor 1504 as it is received, and/or stored in storage device 1510, or other non-volatile storage for later execution.
  • Embodiment 1 is a metrology method comprising: obtaining metrology data relating to a measurement obtained by illuminating a periodic structure comprising at least one pitch with illumination comprising a wavelength and capturing at least a plurality of components of interest of said scattered radiation from said periodic structure at a detection image plane, said illumination comprising at least one incoherent dipole, each said at least one incoherent dipole comprising two mutually incoherent monopoles, said scattered radiation passing through at least one angularly resolved plane between said periodic structure and detection image plane; selecting said wavelength and each said at least one pitch such that mutually coherent interfering components of said components of interest are equidistant to an optical axis of said at least one angularly resolved plane; and determining a parameter of interest of the periodic structure from said scattered radiation.
  • Embodiment 2 is a metrology method as described in embodiment 1, wherein said selecting step further comprises selecting said wavelength and each said at least one pitch such that all said components of interest are reflected and/or scattered to only two scattering locations per measurement direction within said at least one angularly resolved plane.
  • Embodiment 3 is a metrology method as described in embodiment 2, wherein said two scattering locations per measurement direction are symmetrically arranged within said at least one angularly resolved plane with respect to the optical axis.
  • Embodiment 4 is a metrology method as described in embodiment 2 or 3, wherein at least one scattering location of said two scattering locations per measurement direction receives two mutually incoherent components of said components of interest.
  • Embodiment 5 is a metrology method as described in any preceding embodiment, wherein the periodic structure comprises a single pitch, and said plurality of components of interest comprise a zeroth order component for each monopole of said at least one incoherent dipole.
  • Embodiment 6 is aA metrology method as described in embodiment 5, wherein said mutually coherent interfering components comprise a set of a zeroth order and at least one mutually coherent first order for each monopole of said at least one incoherent dipole.
  • Embodiment 7 is a metrology method as described in embodiment 5 or 6, wherein said illumination comprises a single incoherent dipole for measuring in each of two measurement directions, wherein Confidential said single incoherent dipole is oriented at 45 degrees with respect to each of said measurement directions.
  • Embodiment 8 is a metrology method as described in embodiment 7, wherein said mutually coherent interfering components comprise a set of a zeroth order and two mutually coherent first orders for each monopole of said incoherent dipole, one said first order related to one of said two measurement directions, and the other said first order related to the other of said two measurement directions.
  • Embodiment 9 is a metrology method as described in embodiment 7 or 8, comprising selecting said wavelength and said pitch such that mutually incoherent first diffraction orders relating to respective different measurement directions overlap in said at least one angularly resolved plane.
  • Embodiment 10 is a metrology method as described in embodiment 5 or 6, wherein said illumination comprises an incoherent dipole per each of two measurement directions, wherein all four monopoles are mutually incoherent, each of said incoherent dipoles being substantially aligned with a respective measurement direction of said two measurement directions.
  • Embodiment 11 is a metrology method as described in embodiment 10, wherein said mutually coherent interfering components are symmetrically arranged within said at least one angularly resolved plane with respect to the optical axis.
  • Embodiment 12 is a metrology method as described in embodiment 10 or 11, comprising selecting said wavelength and said pitch such that the distance between the monopoles of each said at least one incoherent dipole equals the reciprocal of the pitch in terms of spatial frequency.
  • Embodiment 13 is a metrology method as described in any of embodiments 1 to 4, wherein the periodic structure comprises a first pitch and a second pitch, and said plurality of components of interest comprise only diffraction orders of interest and no zeroth order components.
  • Embodiment 14 is a metrology method as described in embodiment 13, comprising blocking said zeroth order components in the at least one angularly resolved plane.
  • Embodiment 15 is a metrology method as described in embodiment 13 or 14, wherein said illumination comprises a incoherent dipole per each of two measurement directions, wherein all four monopoles are mutually incoherent, each of said incoherent dipoles being substantially aligned with a respective measurement direction of said two measurement directions.
  • Embodiment 16 is a metrology method as described in embodiment 13, 14 or 15, wherein said mutually coherent interfering components are symmetrically arranged within said at least one angularly resolved plane with respect to the optical axis.
  • Embodiment 17 is a metrology method as described in any of embodiments 13 to 16, comprising selecting said wavelength, said first pitch and said second pitch such that, per measurement direction: a first diffraction order resultant from the first pitch and a first monopole of the corresponding incoherent dipole overlaps in said least one angularly resolved plane with another, mutually incoherent, first diffraction order resultant from the second pitch and a second monopole of the corresponding incoherent dipole; and Confidential a first diffraction order resultant from the second pitch and the first monopole overlaps in said least one angularly resolved plane with another, mutually incoherent, first diffraction order resultant from the first pitch and the second monopole.
  • Embodiment 18 is a metrology method as described in any preceding embodiment, comprising non- iteratively reconstructing a field of said scattered radiation; and using said reconstructed field in said step of determining a parameter of interest of the periodic structure.
  • Embodiment 19 is a metrology method as described in embodiment 18, comprising deconvolving an aberration term from the reconstructed field prior to determining the parameter of interest of the periodic structure.
  • Embodiment 20 is a metrology method as described in embodiment 18 or 19, wherein said non- iteratively reconstructing a field comprises Fourier filtering one diffraction order per measurement direction of an image spectrum described by the metrology data or performing a phase-retrieval via a Hilbert transform on said metrology data to determine the electric field.
  • Embodiment 21 is a metrology method as described in any preceding embodiment, comprising blocking unwanted diffraction orders in said at least one angularly resolved plane.
  • Embodiment 22 is a metrology method as described in embodiment 21, comprising using a configurable aperture arrangement to perform said blocking said unwanted diffraction orders.
  • Embodiment 23 is a metrology method as described in any preceding embodiment, wherein said parameter of interest is overlay.
  • Embodiment 24 is a metrology method as described in any preceding embodiment, wherein any said step of selecting said wavelength and each said at least one pitch comprises additionally configuring a distance of each monopole of said at least one incoherent dipole with respect to said optical axis.
  • Embodiment 25 is a metrology method as described in any preceding embodiment, wherein said obtaining said metrology data comprises: illuminating the periodic structure with said illumination comprising at least one incoherent dipole, each said incoherent monopole comprising two mutually incoherent monopoles; capturing scattered radiation from said periodic structure as a result of said illuminating at a detection plane, said scattered radiation comprising said plurality of components of interest.
  • Embodiment 26 is a computer program comprising program instructions operable to perform the method of any of embodiments 1 to 25, when run on a suitable apparatus.
  • Embodiment 27 is a non-transitory computer program carrier comprising the computer program of embodiment 26.
  • Embodiment 28 is a processing device comprising: a processor; and the non-transitory computer program carrier of embodiment 27.
  • Confidential Embodiment 26 is a metrology apparatus being operable to perform the method of any of embodiments 1 to 25 or comprising a metrology apparatus as described in any one of the embodiments 27 to 33.
  • Embodiment 27 is a metrology apparatus as described in embodiment 26, comprising: a substrate holder for holding a substrate; projection optics for projecting illumination onto a substrate; a detector for detecting said scattered radiation at a detection image plane.
  • Embodiment 28 is a metrology apparatus as described in embodiment 27, further comprising an incoherent illumination source for generating said illumination.
  • Embodiment 29 is a metrology apparatus as described in embodiment 27 or 28, comprising a configurable aperture arrangement being operable to block unwanted diffraction orders in dependence with said wavelength and/or each said at least one pitch in said at least one angularly resolved plane.
  • Embodiment 30 is a metrology apparatus as described in any of embodiments 27 to 29, comprising an illumination arrangement configured to emit at least one incoherent dipole, each said at least one incoherent dipole comprising two mutually incoherent monopoles, wherein each monopole of each said at least one incoherent dipole is equidistant from an optical axis of the metrology apparatus.
  • Embodiment 31 is a metrology apparatus as described in embodiment 30, wherein said at least one incoherent dipole comprises a single incoherent dipole oriented at 45 degrees with respect to an apparatus coordinate system defined by two orthogonal measurement directions.
  • Embodiment 32 is a metrology apparatus as described in embodiment 30, wherein said at least one incoherent dipole comprises an incoherent dipole per each of two orthogonal measurement directions, wherein all four monopoles are mutually incoherent, each of said incoherent dipoles being aligned with an apparatus coordinate system defined by the two measurement directions.
  • Embodiment 33 is a metrology apparatus as described in embodiment 30, 31 or 32, wherein said illumination arrangement is configured to vary the distance of each monopole from said optical axis.
  • metalology apparatus may also refer to an inspection Confidential apparatus or an inspection system.
  • the inspection apparatus that comprises an embodiment of the invention may be used to detect defects of a substrate or defects of structures on a substrate.
  • a characteristic of interest of the structure on the substrate may relate to defects in the structure, the absence of a specific part of the structure, or the presence of an unwanted structure on the substrate.
  • the inspection or metrology apparatus that comprises an embodiment of the invention may be used to determine characteristics of structures on a substrate or on a wafer.
  • the inspection apparatus or metrology apparatus that comprises an embodiment of the invention may be used to detect defects of a substrate or defects of structures on a substrate or on a wafer.
  • a characteristic of interest of the structure on the substrate may relate to defects in the structure, the absence of a specific part of the structure, or the presence of an unwanted structure on the substrate or on the wafer.
  • targets or target structures are metrology target structures specifically designed and formed for the purposes of measurement
  • properties of interest may be measured on one or more structures which are functional parts of devices formed on the substrate.
  • Many devices have regular, grating-like structures.
  • structure, target grating and target structure as used herein do not require that the structure has been provided specifically for the measurement being performed.
  • pitch P of the metrology targets may be close to the resolution limit of the optical system of the scatterometer or may be smaller, but may be much larger than the dimension of typical product features made by lithographic process in the target portions C.
  • the lines and/or spaces of the overlay gratings within the target structures may be made to include smaller structures similar in dimension to the product features.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

Abstract

L'invention concerne un appareil et un procédé de métrologie. Le procédé consiste à obtenir des données de métrologie relatives à une mesure obtenue par l'éclairement d'une structure périodique comprenant au moins un pas avec un éclairage comprenant une longueur d'onde et par la capture d'au moins une pluralité de composantes d'intérêt dudit rayonnement diffusé à partir de ladite structure périodique au niveau d'un plan d'image de détection, ledit éclairage comprenant au moins un dipôle incohérent, chacun desdits dipôles incohérents comprenant deux monopôles mutuellement incohérents, ledit rayonnement diffusé traversant au moins un plan à résolution angulaire entre ladite structure périodique et le plan d'image de détection ; à sélectionner ladite longueur d'onde et chacun desdits pas de manière à ce que les composantes interférentes mutuellement cohérentes desdites composantes d'intérêt soient équidistantes par rapport à un axe optique dudit ou desdits plans à résolution angulaire ; et à déterminer un paramètre d'intérêt de la structure périodique à partir dudit rayonnement diffusé.
PCT/EP2025/053868 2024-03-20 2025-02-13 Procédé de métrologie et dispositif de métrologie associé Pending WO2025195690A1 (fr)

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EP24164698.3A EP4621485A1 (fr) 2024-03-20 2024-03-20 Procédé de métrologie et dispositif de métrologie associé
EP24166449.9 2024-03-26
EP24166449 2024-03-26

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